Volumetric quantitative computed tomography of the proximal femur: precision and relation to bone strength

We have developed a three-dimensional computed tomography (CT) scanning and image analysis method for measurement of trabecular and integral bone mineral density (BMD) and geometry in automatically determined femoral-neck and trochanteric subregions of the proximal femur. We measured the correlation of the density and geometry variables to femoral strength assessed in vitro under loading simulating a single-limb condition and a fall to the side. While BMD alone accounted for 48%-77% of the variability in strength for the stance loading configuration, femoral neck cross-sectional area (minCSA) and femoral neck axis length (FNAL) also contributed independently to femoral strength, and a combination of BMD and geometry variables explained 87%-93% of the variance in the data. For the fall loading configuration, trochanteric trabecular BMD alone explained 87% of the variability of strength. The reproducibility in vivo of the technique was assessed in a group of seven postmenopausal women, who underwent repeat scans with repositioning. For trabecular BMD, the precision was 1.1% and 0.6% for the femoral neck and trochanteric subregions, respectively, compared to 3.3% and 1.6% for the corresponding integral envelopes. Thus, trabecular BMD measurements were reproducible and highly correlated to biomechanical strength measurements. These results support further exploration of quantitative CT for assessment of osteoporosis at the proximal femur.